Precision multiturn potentiometer



June 1, 1965 J. w. WEIDENMAN ETAL 3,187,286

PRECISION MULTITURN POTENTIOME'IER Filed July 1, 1963 3 Sheets-Sheet 1 INVENTORS JAMES W. WEIDENMAN GILBERT J. OROZCO i mam .3 ATTORNEY J1me 1965 J. w. WEIDENMAN ETAL. 3,187,286

PRECISION MULTITURN POTENTIOMETER Filed July 1, 1963 5 Sheets$heet 2 13 FIG. 3 FIG. 4

INVENTORS JAMES W. WEIDENMAN GILBERT J.OROZCO BY? Q\\% ATTORNEY June 1, 1965 J. W. WEIDENMAN ETAL Filed July 1, 1963 .3 Sheets-Sheet 3 LU-til i 6 l "J ll I a! 2 32 FIG. 7

INVENTORS JAMES W. WEIDENMAN GILBERT J. OROZCO ATTORNEY United States Patent 3,187,286 PRECISION MULTRTURN PQTENTIGMETER James W. Weidenman, Westbury, Lang island, and Gilbert J. Orozco, New Rochelle, N.Y., assiguors to Litton Industries Inc, Beverly Hills, Calif. Filed July 1, 1963, Ser. No. 292,016 8 Claims. (Cl. 338-149) This invention relates to precision potentiometers more particularly otentiometers of the multiturn type having an elongated resistance element wound on an insulating coil form or core.

A conventional multiturn potentiometer embodies a helically wound resistance, and an input shaft extending through the insulating coil form or core and connected to a rotatable slider arm for supporting a movable contact member engaging the helical resistance element. Normally the potentiometer is of considerable depth or thickness on account of the axial dimension of the core, the length of the bearings for the input shaft and of the support-ing means for the contact slider arm, and the space required for the electrical conductors or leads to the terminals of the potentiometer.

In general terms, the principal object of the invention is to improve the construction of a potentiometer of this type and reduce the thickness or size of the potentiometer by a large factor without sacrificing the precision, reliability and other desired characteristics of the unit. The compact construction resulting from the invention eflYects a saving in space requirements and enables the potentiometer to be used in applications where mounting space is limited.

Another object of the invention is to provide an improved construction for connecting tap leads to the resistance element which permits the convolutions of the helically wound element to be. closely spaced on the insulating core, even substantially in contact instead of being spaced to provide room for the tap connections between adjacent turns of the resistance element.

Anotherobject of the invention is to improve the construction of the coil form or core of a potentiometer so that a tap connection can be made to the underside of the multiturn resistance element wound on said form or core.

A further object of the invention is to provide a compact multiturn potentiometer with a positive stop mechanism for limiting the range of adjustment of the contact member, which includes a stopnut attached to the supporting arm of the contact member, said stopnut being movable within the axial dimensions of the insulating core so that added depth of the unit is not required to accommodate the stop mechanism.

A still further object of the invention is to provide a multiturn potentiometer having a contact member engaging the elongated resistance element which is pivoted on the rotatable contact-supporting arm, and if desired may be readily adjusted to alter the relative positioning of the contactmember and the multiturn resistance element to coordinate the end-of-range positions of the contact and input shaft.

A still further object of the invention is to attach and insulate the contact-supporting arm on the input shaft of a potentiometer in an improved manner.

A feature of the invention relates to a compact multiturn potentiometer in which the turns of the resistance element are closely spaced on the coil form or core, to minimize the thickness of the unit, and the adjustable contact and stop mechanisms are to a great extent confined within the axial dimension or thickness of the coil form or core.

A potentiometer embodying the invention, in the form shown and described herein to illustrate the underlying principles of the invention, comprises a short insulating 3,187,286 Patented June 1, 1965 coil form .or core of channeled cross-section, the multiturn resistance element thereon having minimum spacing between the convolutions of the resistance wire. The general arrangement of core, resistance element and movable contact guide may be similar to that described in the prior US, patent to Weidenman and Rathje, No. 2,871,326 dated January 27, 1959, the disclosure of which is incorporated herein by reference. In accordance with a feature of the present invention, the channel-shaped core is cut away or slotted at its periphery to permit an intermediate tap connection to the underside of the resistance element, thereby avoiding the necessity for spacing the turns of said element to accommodate the tap connection. The contact-supporting arm is preferably attached to and insulated from the input shaft by a construction which reduces the axial dimension of the potentiometer to a minimum, while providing adequate strength and rigidity. In accordance with another feature of the invention, the construction is rendered more compact by pivotally mounting the contact member on the rotatable supporting arm, and by arranging novel stop mechanism for delimiting the range of adjustment of the contact member surrounding the helical resistance element. The stop mechanism preferably includes a stop nut mounted on the rotatable contact-supporting arm diametrically opposite the contact member, whereby the rotating elements carried by the input shaft are dynamically balanced.

The novel features which are believed to be characteristic of the invention, together with further objects and advantages thereof, will be apparent from the following description of an illustrative embodiment thereof shown in the accompanying drawings, wherein- FIGS. 1 and 2 are front and rear views, respectively, of a multiturn potentiometer, a part of the cap or enclosure being broken away in FIG. 2 to reveal the internal construction of the unit;

FIG. 3 is an enlarged cross-sectional view of the potentiometer taken on the line 3-3 of FIG. 2;

FIGS. 4 and 5 are fragmentary views to an enlarged scale, showing a tap connection to the resistance element;

FIGS. 6 and 7 are plan and side elevational views to an enlarged scale of the pivoted contact member of FIGS. 2 and 3; and

FIG. 8 is a detail sectional view taken on the line 8-8 of FIG. 7.

Referring to FIGS. 13 of the drawings, a compact multiturn potentiometer is shown comprising a rotatable input shaft 10 mounted in a hub located behind the seal 11 on the front or base plate 12, A plurality of insulated terminals 13 are connected to the ends of the resistance element of the potentiometer and to one or more tap connections where these are provided as described below. The potentiometer includes a cap or cover member 15 secured in any desired manner to the base plate 12. The potentiometer is shown in FIGS. 1 and 2 approximately twice the actual size of a typical unit in order to show the structural details more clearly.

The potentiometer includes a multiturn resistance element 18, shown as in the form of a compound helix, which is mounted on and afiixed to an insulating ceramic core 19. The convolutions of the helical resistance element 18 are wound on the coil form or core 19 with minimum spacing so that the thickness or axial length of the core may be only a fraction of an inch for a 10- turn unit, thus permitting a novel pivoted contact arrangement instead of the slider contact assembly used heretofore in multiturn potentiometers. An insulating guide helix 21 for the movable contact member is wound over the turns of the resistance element 18. While other forms of resistance elements may be employed, the preferred construction shown except for the close spacing of 1 the turns of the resistance element is similar to that described and claimed in the above-mentioned Weidenman and Rathje patent.

The insulating coil form or core 19 is clamped to the hub of the base plate 12 by clamping screws 23, as shown in FIGS. 2 and 3, said clamping screws being threaded into a concentric ring 24 mounted on said hub. The ring 24 engages the edge of a locking ring 25 disposed in a groove in the hub of the base plate 12 as shown in FIG. 3. The insulating core 19 is of U-shaped or channelled cross-section with inwardly extending radial flanges and is provided with a radial groove 28 on the inside face to provide space for the terminal leads or conductors 29 extending between the resistance element 18 and the terminals 13/ As shown in FIGS. 2, 6 and 7, a pivoted contact member 31 is mounted on an offset lug or extension 32 of the rotatable supporting arm 33 carried by the input shaft 13. Thus the rotation of the input shaft 13 serves to shift the point of contact between the contact member 31 and the resistance element 18 in the usual manner. The contact-supporting arm 33 is electrically connected through a contact brush (not shown) to one of the terminals 13. The rotatable arm 33 is also provided with a second offset portion or lug 34, preferably arranged diametrically opposite the offset portion 32. In this manner the rotatable elements of the potentiometer are dynamically balanced when the input shaft is rotated at a relatively high speed. The stop means for limiting the rotative adjustment of the contact member 31 comprises a threaded stop nut 36, preferably mounted on the oifset portion 34 of the contact-supporting arm 33 and insulated from said arm as indicated at 37.

In accordance with a feature of the invention, the stop means is arranged adjacent to the helical resistance element 1% and within the axial dimensions of said element so that additional space is not required for said element along the length of the shaft 13, thus rendering the construction of the unit more compact. As shown the stop nut 36 is provided with threads on the outside face or surface of the stop nut which are adapted to engage circumferential threads 38 formed on the inside of the cap 15, so that the stop nut 36 moves laterally on the lug 34 in a direction parallel to the axis of the shaft 10 as the shaft is turned. Two fixed stop members such as that indicated at 41 in FIG. 3 are provided in the path of the stop nut 36 as it reaches its two extreme positions of adjustment.

In order to rigidly attach the rotatable contact arm 33 to and insulate it from the input shaft 10, a disc-shaped member 43, having a notched groove around its periphery, is attached to the inner end of the shaft 10. The contact arm 33 is provided with a sim-ilarlynotched circumferential groove in a concentric opening therein as shown in FIGS. 2 and 3. In order to attach the contact arm 33 to the disc 43, plastic insulating material 44 is molded in situ between the edges of the grooved portions of the elements 33 and 43 so that the arm 33 is rigidly attached to the shaft It) while holding the depth or axial dimension of the assembly to a minimum. On account of the notches formed in the attached members 33 and 43, the interposed insulating material 44 is subjected to compression when the stop nut 36 engages one of the stop members 41, and, since the material 44 withstands compressive forces, distortion of the angular relationship between the arm 33 and the shaft 10 is prevented.

In accordance with another important feature of the invention, tap connections to the resistance element 18 are made by welding a fine jumper wire to the inside of said element at the desired point. In order to exposethe inside surface of the resistance element 18 for attachment of the tap connection, the insulating coil form or core 19 has a U-shaped or channeled cross-section with inwardly projecting integral sides of considerable depth, so that the core can be slotted as indicated at 46 in FIGS. 3, 4 and 5, across the entire width or thickness of the core.

tached solder lug 48, which is cemented to the core at the slot 46. A wire jumper 49 is welded to the precise predetermined tap point on the resistance element 18 and to the connector 47. This construction eliminates the necessity for spacing the adjacent turns of the resistance element 13 to provide space for running the tap leads from the point of connection on said element and permits the turns to be spaced very closely on the surface of the coil form or core 19.

Where the input shaft 13 of the potentiometer is likely to be subjected to excessive transverse stresses in use, the usual ball-bearings 51 and 52 between the shaft and the hub in the base plate 12 may be supplemented by closely fitted bushings or sleeve bearings 53 and 54 located out-' side of the ball-bearings as shown. The bearing surface dimensions of the bushings 53 and 54 are such that shaft 10 is normally supported exclusively by the ball-bearings 51 and 52; however when the outer end of the shaft 10 is subjected to excessive force in a transverse or radial direction which would cause bending of the shaft 10, the bushings provide a solid contact between the hub and the shaft 10, and prevent damage to the balls or races of the ball-bearings 51 and 52. It will be understood that the shaft 13 may be provided with shaft seals, such as that indicated at 55 in FIG. 3, whenever the potentiometer is subjected to adverse atmospheric conditions in use. Such seals form no part ofthe present invention since conventional seals have been widely used, and require no description.

In accordance with another feature of the invention, on account of the small depth and compact spacing of the helical resistance element 18, the contact member 31 is pivotally mounted on the offset supporting lug 32 of the supporting arm 33, instead of being attached to the usual slider assembly. As shown more clearly in FIGS. 6, 7 and 8, the contact member 31 preferably includes an offset projecting portion 56 at the tip end of the contact member which engages the surface of the resistance element 18 and is guided along the length thereof by the guide helix 21. As shown the contact member 31 is supported on the lug 32 by a pivot assembly consisting of opposed conical bearing members 58 and 59 carried by the upper and lower extensions respectively of a U-shaped bracket 61 to which the contact member 31 is Welded or soldered. The supporting lug 32 is provided with sapphire jewel bearings 62 forming frictionless bearings for the bracket 61 and attached contact 31. A jumper wire 63 is soldered to the contact member 31 and to the arm 33 to provide a low-resistance connection between the contact member and the potentiometer terminal 13. In order to permit a small lengthwise adjustment of the contact tip 56, to correct its position at one end of the range of adjustment of the potentiometer, in accordance with the invention the pivotal support for the contact member is laterally adjustable for a fixed, permanent re-adjustment of the pivot point. In the construction shown in FIGS. 6 and 7, the lug or bracket 32 is shown as provided with a transverse slot 65 adapted to receive the tip of a screw driver or similar tool. The slot 65 reduces the cross-section of the lug 32 at this point so that the screw driver may be used to distort the outer end of the lug which carries the pivot of the contact member 31, as indicated by the outline 66 in dotted lines. In this manner a permanent micrometric adjustment of the point of contact between the contact member 31 and the resistance element 18 may be made. Other suitable or equivalent methods of adjusting the contact 31 may be employed.

lt will be evident that the invention providesa precision potentiometer of exceedingly compact, rugged construction. In accordance with the teaching of the invention,

the multiturn resistance element is substantially reduced in size from the conventional construction, and the novel contact and stop assemblies are arranged substantially Within the thickness dimension of the insulating core without sacrificing precision or reliability.

It is to be understood that the above described arrangement is illustrative of the application of the principles of the invention. Other arrangements within the scope of the invention may be devised by those skilled in the art. Thus, by way of example and not of limitation, the form and mounting of the multiturn resistance element may be modified, the construction and mounting of the contact member 31 may be of any suitable design and the contact may be a part of a slider assembly instead of being pivoted as shown, where the size of the unit is not a principal consideration. It Will also be understood that certain features of construction may be employed in a potentiometer embodying the invention without one or more of the other novel features described in the foregoing detailed specification. Accordingly it is evident that various changes may be made in the present invention Without departing from the spirit of the invention as defined in the appended claims.

What is claimed is:

1. In a multiturn potentiometer, in combination,

a helically wound multiturn resistance element,

a rotatable input shaft concentric with said resistance element,

a rotatable contact carrier member attached to said input shaft, said carrier member having a projection extending parallel to said input shaft, said projection having a deformable tip portion of reduced crosssection, and

a contact member pivoted on said deformable tip portion and engaging said multiturn resistance element, said contact member extending laterally of said contact carrier member to provide adjustment of the point of contact along said resistance element as said tip portion of the carrier member is distorted, during final assembly and testing of the potentiometer.

2. In a multiturn potentiometer having a helically wound multiturn resistance element and a movable contact member engaging said element, the improvement comprising,

a hollow cylindrical insulating core having at least one radial flange and supporting said resistance element, said cylindrical core being slotted at its periphery across the width of the several turns of the core to form a slot through the thickness of the resistanceelement supporting portion of said core and a portion of said radial flange less than the entire radial extent of said flange, and exposing the underside of said resistance element, and

a tap connection to an intermediate point of said resistance element disposed in said slot.

3. In a multiturn potentiometer, a multiturn resistance element, a hollow cylindrical insulating core having inwardly extending radial flanges at each end thereof and supporting said resistance element on the outside periphery thereof, said core being provided with a longitudinal slot extending through the entire thickness of said core throughout the length of the slot to form an opening exposing the underside of all of the turns of said resistance element, said slot extending only partially through the radial extent of at least one of said radial flanges, a contact terminal disposed in said opening, and a welded tap connection between said terminal and the underside of the resistance element intermediate the ends of said element.

4. In a multiturn potentiometer having a helically Wound multiturn resistance element and an input shaft concentric with said resistance element, the improvement comprising,

a rotatable supporting member attached to said input shaft, said supporting member including two diametrically opposed offset portions overlying the external periphery of said resistance element,

a contact mounted on one of said offset portions of the supporting member and engaging the resistance element, and

a stop member for limiting the shaft rotation mounted on the other offset portion of the supporting member.

5. In a multiturn potentiometer having a helically wound multiturn resistance element, and an input shaft concentric with said resistance element, the improvement comprising,

a rotatable arm attached to said input shaft,

a stop-nut provided with external screw threads slidably mounted on said rotatable arm,

means providing a fixed circumferential thread surrounding said rotatable arm with said thread adapted to be engaged by the threads on said stop-nut, and

a fixed stop in the path of said stop-nut to limit the rotation of said input shaft.

6. In a multiturn potentiometer having a helically Wound multiturn resistance element and an input shaft concentric with said resistance element, the improvement comprising,

a cup-shaped, internally threaded cover member for said potentiometer with threads on said cover member surrounding and closely spaced from the convolutions of said resistance element,

a threaded stop-nut carried by said input shaft and engaging the threads in said cover member, and

a fixed stop member cooperating with said stop-nut to limit the rotation of said input shaft.

7. In a potentiometer having an elongated resistance element and a movable contact member for engaging said element, the improvement comprising,

an input shaft for actuating said contact member,

a disc member attached to the end of said input shaft,

a supporting arm for said contact member provided With an opening in alignment with said disc, and

a body of molded insulating material in said opening for insulating said rotatable supporting arm and locking said arm to the disc and input shaft.

8. A potentiometer according to claim 7, in which the abutting edges of said disc and arm are notched to provide positive resistance to displacement of the arm on said shaft as a result of a twisting force applied to said shaft when the arm is locked against rotation.

References Cited by the Examiner UNITED STATES PATENTS 1,621,466 3/27 Jenkins 338- 2,423,973 7/47 Halford 308-35 2,839,643 6/58 Vercesi 338-149 X 2,871,326 1/59 Weidenman et al 338-l48 2,899,660 8/59 Ford 338-443 2,900,614 8/59 Gach et a1 338-149 2,961,626 11/60 Moore et a1. 338-143 3,069,646 12/62 Hardison et a1. 338162 RICHARD M. WOOD, Primary Examiner. ANTHONY BARTIS, Examiner. 

5. IN A MULTITURN POTENTIOMETER HAVING A HELICALLY WOUND MULTITURN RESISTANCE ELEMENT, AND AN INPUT SHAFT CONCENTRIC WITH SAID RESISTANCE ELEMENT, THE IMPROVEMENT COMPRISING, A ROTATABLE ARM ATTACHED TO SAID INPUT SHAFT, A STOP-NUT PROVIDED WITH EXTERNAL SCREW THREADS SLIDABLY MOUNTED ON SAID ROTATABLE ARM, MEANS PROVIDING A FIXED CIRCUMFERENTIAL THREAD SURROUNDING SAID ROTATABLE ARM WITH SAID THREAD ADAPTED TO BE ENGAGED BY THE THREADS ON AID STOP-NUT, AND A FIXED STOP IN THE PATH OF SAID STOP-NUT TO LIMIT THE ROTATION OF SAID INPUT SHAFT. 